It has long been recognized that solar power provides a clean, efficient, inexpensive and renewable energy source that can be used for many different applications. Solar energy is believed to hold the future of the world's energy needs once it can be effectively harnessed. This has led to a tremendous amount of research and investment in solar energy and its conversion to useful energy such as electricity through photoelectric solar cells, thermal energy in the form of solar water and space heaters for heating applications, and energy storage that can be used to power domiciles and commercial buildings. There has been less research, however, into using the sun's energy for cooling applications. The present invention seeks to provide a significant advance over the prior art and serves to convert the sun's heat into a system that can provide, among other things, a cooling system.
Mechanical cooling systems are also well known in the art. In a refrigeration system using a basic vapor compression cycle, cooling is achieved in an evaporator as low temperature refrigerant such as Freon enters the evaporator as a mixture of liquid and vapor and is completely vaporized by a thermal input. The remaining equipment in the system attempts to reclaim the refrigerant and restore it to a condition that can be used again to provide cooling. The vapor exiting the evaporator in a saturated or slightly superheated condition enters a compressor that raises the pressure and, consequently, the temperature of the refrigerant. The high pressure hot refrigerant enters a condenser heat exchanger that uses ambient air or water to cool the refrigerant to its saturation temperature prior to fully condensing to a liquid. The high-pressure liquid is then throttled to a lower pressure, which causes some of the refrigerant to vaporize as its temperature is reduced. The low temperature liquid that remains is available to produce useful refrigeration.
FIG. 1 depicts a typical, single-stage vapor-compression system. Such systems typically have four main components: an evaporator 10, a compressor 20, a condenser 30, and an expansion valve 40 (also called a throttle valve). Circulating refrigerant enters the compressor in the thermodynamic state known as a saturated vapor and is compressed to a higher pressure, resulting in a higher temperature as well. The hot, compressed vapor is then in the thermodynamic state known as a superheated vapor and it is at a temperature and pressure at which it can be condensed with typically available cooling water or cooling air. That hot vapor is routed through a condenser where it is cooled and condensed into a liquid by flowing through a coil or tubes with cool water or cool air flowing across the coil or tubes. This is where the circulating refrigerant rejects heat from the system and the rejected heat is carried away by either the water or the air (whichever may be the case).
The condensed liquid refrigerant, in the thermodynamic state known as a saturated liquid, is next routed through an expansion valve where it undergoes an abrupt reduction in pressure. That pressure reduction results in the adiabatic flash evaporation of a part of the liquid refrigerant. The auto-refrigeration effect of the adiabatic flash evaporation lowers the temperature of the liquid and vapor refrigerant mixture to where it is colder than the temperature of the enclosed space to be refrigerated.
The cold mixture is then routed through the coil or tubes in the evaporator. A fan may be used to circulate the warm air in the enclosed space across the coil or tubes carrying the cold refrigerant liquid and vapor mixture. That warm air evaporates the liquid part of the cold refrigerant mixture. At the same time, the circulating air is cooled and thus lowers the temperature of the enclosed space to the desired temperature. The evaporator is where the circulating refrigerant absorbs and removes heat which is subsequently rejected in the condenser and transferred elsewhere by the water or air used in the condenser. To complete the refrigeration cycle, the refrigerant vapor from the evaporator is again a saturated vapor and is routed back into the compressor.
The major energy input to a vapor compression refrigeration system is the mechanical power needed to drive the compressor. The minimum compressor power is given in Equation 1. The compressor power requirement is substantial because the specific volume of the refrigerant vapor, v, is large. Additional power is needed to operate the fans or pumps to move the external fluids.
                                          W            .                                comp            ,            min                          =                              m            .                    ⁢                                    ∫                              P                1                                            P                2                                      ⁢                          v              ⁢                                                          ⁢                              ⅆ                P                                                                        (        1        )            
The important consideration for a vapor compression refrigeration system is its coefficient of performance (COP), defined as the ratio of the cooling capacity to the total electrical power required. A COP for a system providing refrigeration at −10° C. (14° F.) while rejecting heat to a temperature at 30° C. (86° F.) is approximately 3. The system COP diminishes from that level when the electrical power required for moving the external fluids is accounted for in the coefficient of performance. If the energy requirements could be accomplished by solar energy, or at least a major portion of the energy requirements satisfied by solar power, the COP would increase dramatically and greatly improve the efficiency and cost of the system. The present invention is directly to improving the efficiency of existing cooling systems with a solar powered compressor that can be substituted for or used along with an existing compressor in a cooling system to increase the cooling and reduce costs.